Production of Uniform Dense Titanium Plasmas for Experiments on Atlas

Finhole camera imaging of an ablative capillary discharge

investigated for the development of a soft x-ray laser

R Dussart, S. Gatze, D. Hong, J. Pons, C. Cachoncinlle,

J.-M. Pouvesle, C. Fleurier

GREML, UMR6606 CNRSKJniversite d'OrlCans, B.P. 6744,

45067 OrlCans Cedex 2, France

Abstract

End-on images of an ablative capillary discharge have

been obtained using a time resolved pinhole camera. This

experiment was motivated by the feasibility study of a soft

x-ray laser in a highly ionized carbon plasm created by

electrical discharges. Such laser effects have already been

observed in laser pumped x-ray laser experiments [l]. The

population inversion can be obtained by a collisional

recombination scheme, which is favored by a rapid cooling of

the fully stripped carbon plasma

In our experiment, the plasma was created by injecting

a high current pulse of several tens of kA in 100 m into a

1 mm diameter capillary initially under vacuum. It was

composed of highly ionized carbon and stripped hydrogen

provided by the polyethylene capillary wall. Soft x-ray

production could be spatially localized by analyzing images

obtained by means of a 0.1 pm polyimide filter, which was

installed between the discharge and the camera. The

,+olyimide filter had a good transmission for soft x-rays fkom

the 10-20 nm wavelength range. Spectroscopic investigations

had been previously performed to analyze the plasma

emission [2].

The time evolution of the plasma radial distribution

was determined for two capillary lengths (10 and 16 mm). For

a 23 kA injected current pulse, an emission ring mostly

composed of W emitters showed the ablated material

provided by the wall. For a 48 kA injected current pulse, the

profiles were analyzed in details showing the plasma heating

followed by its cooling due to thermal diffusion from the

capillary wall. No evident z-pinch occurred on the frst

current pulse. The results of time resolved spectra were

consistent with those observed with pinhole experiments.

Different